1. Field of the Invention
The present invention relates to a method for modulating digital data and apparatus therefor and particularly, to a method for modulating digital data and apparatus therefor which determines digital data stream coded by Run Length Limited (hereinafter as RLL) swiftly and precisely so as to record data in a recording medium (also referred to herein as record medium).
2. Description of the Background Art
Generally, Non-Return-to-Zero-Inverse (hereinafter NRZI) code shows that no change is in magnetic flux of a record medium if the signal detected in the record medium is a binary number xe2x80x980xe2x80x99 and that the direction of magnetic flux recorded in the record medium is reversed if the signal detected in the record medium is a binary number xe2x80x981xe2x80x99 thus to record data in the record medium and detects or regenerate the recorded signal.
Recently, by the Run Length Limited (Hereinafter as RLL) code in which the concept of the NRZ code is expanded, a 8 bit data is modulated to a 16 bit data and the modulated code word is recorded in a record medium. At this time, the code word should satisfy these two restriction conditions. X
The first restriction condition is that among bits having consecutive 1s, at least a bit having xe2x80x980xe2x80x99 value bit should exist. For instance, a data bit becomes three times as large as a data record density stored without a specific condition and accordingly, the data is recorded in the record medium with a high record density. At this time, on the first restriction condition, the data recorded in the record medium should be positioned in the distance so that the magnetic flux polarity of the data bit can be sorted even though the data is recorded in the record medium with a high record density. Namely, the first restriction condition is that bits having a certain xe2x80x980xe2x80x99 bit value in the record medium are recorded and symbols do not intervene each other when the recorded data is regenerated.
Also, the second restriction condition is that the numbers of bits having 0 value bits should not be many among the bits having consecutive 1 value bits. If the bits which have 0 value are not spread but is formed in a stream, the clock which generates a phase lock circuit is not motivated. Therefore, clock signals can be restored from the regenerated data by locking the phase lock circuit in the position where transition of the regenerated data is performed.
However, the data stream modulated satisfying the restriction conditions generally includes DC component. If the data stream in which the DC component is not removed is recorded in the record medium, when the data stream is regenerated, error signals such as tracking errors of the record medium are generated and accordingly, normal output of regeneration data can not be performed. Namely, the DC composition signals interrupt the recorded digital signals from dealing with low frequency components normally. By removing the low frequency components, consecutive tracking controlling is enabled and accordingly when the data recorded in the record medium is detected through the optical recording carrier, the recorded data can be normally regenerated. Therefore, if the low frequency components are controlled properly, tracking controlling of the record medium is capable of not being influenced on the low frequency components.
Therefore, to solve the problems that the DC components are included in the modulated data, the Digital Sum Value (hereinafter as DSV) of modulated data stream controlling technique is developed. Here, the DSV, for example, in case of using NRZI modulating method, is obtained by modulating the m units of source words into n units of channel words and adding up the channel words. At this time, the NRZI modulating method allocates a binary number xe2x80x980xe2x80x99 bit of the channel words to xe2x88x921 value and a binary number xe2x80x981xe2x80x99 bit is allocated to a xe2x80x98+1xe2x80x99 value. Therefore, a digital data stream having a small DSV becomes a digital data stream containing small amount of DC component.
The method for controlling the DSV of digital data stream in accordance with the conventional art is described as follows.
FIG. 1a and FIG. 1b are tables showing the first and second digital data stream to describe the method on how to determine a digital data stream according to the conventional art and each table includes a bipolar code stream obtained from each bit of the first and second digital data stream, the DSV obtained from the bipolar code stream and an absolute value of the DSV and the squared value of the DSV obtained from the DSV.
(1) Method Using the Value of DSV
For example, in case of comparing the DSV value of each of the first and second data stream for 4 bites, as shown in FIG. 1a, the DSV of the first digital data stream is 4 and as shown FIG. 1b, the DSV of the second digital data stream is 0. Therefore, the second digital data stream is determined as a code word since the small DSV of the second digital data stream is fit to the data stream condition having a small DC component.
(2) Method Using the Absolute Value of DSV
In case of comparing the absolute value of the DSV for 4 bites, as shown in FIG. 1a, the absolute value of the DSV of the first digital data stream is 50 1+0+1+0+, . . . , +2+3+4), and as shown in FIG. 1b, the absolute value of the DSV of the second digital data stream is 39 (1+0+1+0, . . . , +0+1+0). Accordingly the second digital data stream is determined as a code word since the small DSV of the second digital data stream fits the data stream condition having a small DC component.
(3) Method Using Squared Value of DSV
In case of comparing the squared value of the DSV for 4 bites, as shown in FIG. 1a, the squared value of the DSV of the first digital data stream is 118 (1+0+1+0+, . . . , +4+9+16), and as shown in FIG. 1b, the squared value of the DSV of the second digital data stream is 92 (1+0+1+0, . . . , +0+1+0). Accordingly, the second digital data stream is determined as a code word since the small DSV of the second digital data stream fits the data stream condition having a small DC component.
(4) Method Using Critical Value of DSV (a Method Thereby for Determining a Digital Data Stream with a Small DC Component as the Code Word According to the Number of the DSV Larger Than the Level of a Certain Critical Value)
FIG. 2a and FIG. 2b are graphs showing each size of the DSV of the FIG. 1a and FIG. 1b according to the conventional art. For example, the number of the DSV having a bigger value than the level of M=|xe2x88x92M|=2 as shown in FIG. 2a, for the first digital data stream is 15 times, and for the second digital data stream is 12. Therefore, the second digital data stream having a small number of the DSV which are larger than a certain critical level is determined as a code word.
It is described that the conventional modulating method for a digital data stream determines by using the DSV calculated in terms of bit, the absolute value of the DSV and the squared value of the DSV. However, actually, the digital data stream is determined by using the calculated value in terms of bite or word.
However, the conventional data modulating methods described above have a disadvantage that the circuit is large and accordingly, the composition of the hardware is very complicated and the efficiency is not good compared to the size of the circuit since many multipliers are necessary to select the second digital data stream when it is realized in the form of hardware.
On the other hand, to reduce the influence of noise such as the DC component, there is a modulating method of maintaining the DSV by adding a merging bit to the source data stream, but the method has a disadvantage of reducing modulating efficiency of the source data stream and of reducing record density.
One object of the present invention is to provide a method for modulating digital data and apparatus therefor for determining the digital data stream having the minimum DSV swiftly and precisely.
Another object of the present invention is to provide a method for modulating digital data and apparatus therefor for determining the digital data stream having the minimum DSV using weight values corresponding to the DSV and preset critical value swiftly and precisely.
To achieve these and other objects, the digital data modulating method in accordance with an embodiment of the present invention includes the steps of: comparing a preset critical value and DSV of a certain digital data stream; computing the penalty of the digital data stream by multiplying the number of the time that the DSV of the digital data stream is larger than the critical value by a preset weight value of the critical value; and comparing the penalty of the digital data and a penalty of another digital data stream and determining a digital data stream with a smaller penalty for the digital data stream.
The apparatus for modulating digital data according to an embodiment of the present invention includes: a DSV calculating unit for computing DSV of the inputted digital data; a DSV lever detector for outputting the weight value corresponding to the critical values comparing the DSV and the preset critical value; and a penalty generating unit for generating a penalty of the digital data stream using the DSV detected by the level detector.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.